1. Field of the Invention
The present invention relates to a dust-detection technology for an image processing apparatus, such as a digital copying machine, that includes a sheet-through document feeder (SDF).
2. Description of the Related Art
In recent years, an image processing apparatus adopting a sheet-through scan system, which is called a sheet-through document feeder (SDF), has been used as one of the image processing apparatuses. The image processing apparatus adopting the sheet-through scan system automatically feeds an original with the SDF and causes the automatically fed original to pass on an SDF original glass where a carriage, which holds a light source and a plurality of mirrors, is located. An image of the original is reflected on the mirrors. The image processing apparatus focuses the image of the original on a charge coupled device (CCD) via a lens to thereby output the image of the original as image data. An image processing apparatus adopting a conventional system reciprocatingly moves a carriage in a sub-scanning direction with respect to an original, which is placed on a contact glass, to read an image of the original. Compared with the image processing apparatus adopting the conventional system, the image processing apparatus of the sheet-through scan system has an advantage that a structure thereof is simplified.
In the image processing apparatus adopting the sheet-through scan system, there is a deficiency in that a deposit such as dust moves onto the SDF original glass from an original to cause a vertical streak on an image. This is because, in the sheet-through scan system, since the original moves, images of the deposit or a scratch are continuously formed in the sub-scanning direction on the SDF original glass.
The image reading apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-185728 mechanically moves an original reading position when dust, a scratch, or the like is detected and finds a position where no dust, scratch, or the like is present. When dust, a scratch, or the like is detected in all areas of reading positions, the image reading apparatus urges a user to clean a reading window glass.
However, the image reading apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-185728 requires an additional mechanism to find a position where no dust, scratch, or the like is present. This leads to an increase in cost.
When dust, a scratch, or the like is present in areas of reading positions, since the dust, the scratch, or the like is recognized as a character, edge enhancement occurs.